Heat the olive oil in a large skillet over medium-high heat until shimmering
Add the onion and sauté the onions until translucent (apx 3-4 minutes)
Add the garlic and continue to sauté until raw smell is gone (apx 1-2 minutes)
Add the shredded turkey and continue to sauté for another minute
IF USING: add the chopped vegetables and continue to sauté for another minute
Add the gravy and parsley to the mixture and mix until fully incorporated - Adjust seasoning with salt and pepper to taste - Remove from heat and set aside until needed
Add the half and half to the leftover mashed potatoes and thoroughly combine (leftover mashed potatoes will stiffen in the fridge so this is just to 'loosen' them up)
Cover and place the mashed potatoes in the microwave on high for 1 minute - Add the cream cheese and stir in until well incorporated (depending on your microwave you may have to heat the potatoes a little longer for the cheese to melt - BE CAREFUL, the potatoes just need to be warm enough to 'melt' the cream cheese so it can be incorporated not HOT)
Lightly grease a 9x13 baking dish and spread ¼ of the mashed potatoes evenly across the bottom - Spread the turkey mixture (from Steps 2-7) over the top
Cover with the remaining mashed potatoes - Sprinkle the parmigiano-reggiano over the top
Bake in the top third of your oven for 30 minutes or until the top is bubbly and golden brown
Serve hot garnished with additional grated parmigiano-reggiano and chopped parsley if desired